This protocol focuses on the regulation of 1,25(OH)2D in patients with humoral hypercalcemia of malignancy (HHM) as composed to patients with hyperparathyroidism (HPT). Although patients with HPT and HHM share certain similarities (hypercalcemia, renal phosphorus wasting and osteoclastic bone resorption, they also differ in important ways. For example, patients with HPT display elevations in the level of the active vitamin D metabolite, 1,23 (OH)2D whereas those with HHM display marked reductions. The reasons for the differences in the two syndromes remain unexplained, but are critical to understand in order to further differentiate between the usually coupled mechanisms of bone formation and resorption. The specific aim of this study is to determine whether renal 1,25 vitamin D production is stimulated by PTHrP in patients with hypercalcemia of malignancy.